It is common in testing devices used for the testing and calibration of instruments such as flow volume integrators and pressure and temperature chart recorders for the motor of the testing device to rotate a number of revolutions thus causing the instrument's shaft to rotate an equal or a proportional number of revolutions, either in clockwise or counter-clockwise direction. Furthermore the testing device may be equipped with a device to indicate the resistance caused by the instrument's shaft relative to the free running of the motor when not under any load.
Devices of this type perform only two functions--to simulate the rotation of a meter instrument drive and to indicate the level of drag caused on or by the instrument's shaft and they are inefficient, error prone and very unreliable because:
(1) the counter of the testing device keeps track of the number of revolutions travelled by the motor shaft only but not that of the instrument under test;
(2) there is no means to verify the integrity of the flow sensing switches in electromechanical or electronic instruments while the testing device is running;
(3) there is no means to verify if the correct number of electrical impulses are transmitted to and received by the instrument under test. These factors directly affect the registration of the instrument under test, thus its accuracy. They are, moreover, not suitable for automatic operation because they do not have any provision for such operation or necessary interface(s) to a computer.
They cannot perform any diagnostic tests other than for the drag of the instrument's shaft. Also, all data have to be transcribed manually, the instrument's error computations have to be done manually and no data storage and retrieval capability is provided for.
The use of data obtained by using these devices to evaluate the performance of the instrument under test requires a number of assumptions which are sometimes erroneous. The results obtained are, therefore, unreliable.
The above disadvantages are overcome by the automatic testing and calibrating system of the present invention which provides in various aspects of the invention for (1) continuous monitoring of flow volume sensing switch(es), 2) continuous monitoring of electrical impulses transmitted by the flow sensing switch(es), (3) continuous monitoring of electrical impulses the instrument receives from the flow sensing switch(es), (4) continuous monitoring of other parameters such as pressure and temperature, etc., (5) continuous monitoring the electrical impulses representing the uncorrected volume simulated by the system, (6) continuous monitoring the electrical impulses representing the uncorrected flow volume received and registered by the instrument, (7) continuous monitoring the electrical impulses representing the corrected flow volume computed, registered and displayed by the instrument, (8) computing for the referenced corrected flow volume using an industry standard flow volume equation applicable to the fluid to be measured and the primary measuring device used, (9) comparing the corrected volume as registered by the instrument to the referenced corrected volume as computed by the system to determine the instrument's error thereby improving test reliability, and assuring data integrity and reducing instrument verifying and calibrating time and cost, whilst it is also portable.
Thus according to the present invention, there is provided a system for verification of instruments used on meters to measure fluid passing through a pipeline, said system comprising:
a stepping motor which, when rotated, drives a drive dog which in turn drives the instrument's shaft or activates one or more proximity sensing switch(es) whose electrical impulse represents a certain volume of fluid flowing through the pipeline; a stepping motor driver; a computer interface allowing the computer to control the stepping motor driver; and physical means for the computer to receive electrical impulses representing various measurement parameters back from the instrument.
In another embodiment of the invention there is provided a method for calibrating and adjusting a fluid flow measuring device having flow sensing switches and having means to generate first electrical signals representative of fluid flow, the method comprising controllably and forcibly driving the flow sensing switches of the measuring device in a manner corresponding to a reference volume of flow, producing second electrical signals representative of the reference volume, receiving and processing the first electrical signals from the measuring device to produce a corrected or uncorrected volume signal, comparing the corrected or uncorrected volume signal to the reference volume signal and producing output representative of the comparison; and adjusting the flow measuring device using the output.